When two wireless devices (WD) in a cellular system wish to exchange information, the information may be transmitted on an uplink from the source WD to the network and then echoed on a downlink from the network to the destination WD; this mode of operation may be referred to as Indirect Device-to-Device (ID2D) communications. While information may be routed through the network if the communicating devices are far enough apart that they are beyond the reach of their transmitters, routing through the network may also occur in some cellular networks even if the devices are in close proximity to each other. It may be beneficial to define a mode of operation that enables Direct Device-to-Device (DD2D) communications between wireless devices that are in close proximity (e.g. close enough to be within the reach of each other's transmitters) thus avoiding the route through the network.
As used herein, the term “user equipment” (alternatively “UE”) might in some cases refer to mobile devices or wireless devices such as mobile telephones, personal digital assistants, handheld or laptop computers, and similar devices that have telecommunications capabilities. The terms UE, mobile device, and wireless device may be used interchangeably herein. Such a UE might include a device and its associated removable memory module, such as but not limited to a Universal Integrated Circuit Card (UICC) that includes a Subscriber Identity Module (SIM) application, a Universal Subscriber Identity Module (USIM) application, or a Removable User Identity Module (R-UIM) application. Alternatively, such a UE might include the device itself without such a module. In other cases, the term “UE” might refer to devices that have similar capabilities but that are not transportable, such as desktop computers, set-top boxes, or network appliances. The term “UE” can also refer to any component that can terminate a communication session for a user. Also, the terms “user equipment,” “UE,” “user agent,” “UA,” “user device,” “wireless device”, “WD”, and “mobile device” might be used synonymously herein.
As telecommunications technology has evolved, more advanced network access equipment has been introduced that can provide services that were not possible previously. This network access equipment might include systems and devices that are improvements of the equivalent equipment in a traditional wireless telecommunications system. Such advanced or next generation equipment may be included in evolving wireless communications standards, such as Long-Term Evolution (LTE) and LTE-Advanced (LTE-A). For example, an LTE or LTE-A system might be an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and include an E-UTRAN node B (or eNB), a wireless access point, or a similar component. As used herein, the term “base station” refers to any component of the wireless network, such as a traditional base station, a wireless access point, or an LTE or LTE-A node B or eNB, that creates a geographical area of reception and transmission coverage allowing a UE or a relay node to access other components in a telecommunications system. The geographical area of reception and transmission coverage provided by a base station may be referred to herein as a cell.